Tokkai Hei8-109818, published by the Japan Patent Office in 1996, discloses a method of estimating a trapped particulate matter amount in order to regenerate a diesel particulate filter (hereafter referred to as DPF).
The DPF is provided in an exhaust passage of a diesel engine to trap particulate matter contained in the exhaust gas that is discharged from the diesel engine. When the DPF traps a predetermined amount of particulate matter, the trapped particulate matter is burned by means of an operation to raise the temperature of the DPF, whereupon the DPF is once again able to trap particulate matter. This process is known as DPF regeneration. The DPF temperature is raised by manipulating the fuel injection amount or injection timing of the diesel engine, or by heating the DPF using a heating device.
The determination as to whether or not to regenerate the DPF is made on the basis of the amount of particulate matter deposited in the DPF. In the prior art, the particulate matter deposit amount is estimated on the basis of pressure loss generated in the exhaust gas flow by the DPF. More specifically, a differential pressure between the pressure of the exhaust passage upstream of the DPF and the pressure of the exhaust passage downstream of the DPF is detected by a differential pressure sensor, and when the differential pressure reaches a predetermined value, it is determined that a predetermined amount of particulate matter is trapped in the DPF.
Regardless of the method that is applied to regenerate the DPF, more energy is consumed during regeneration to increase the temperature of the DPF than during non-regeneration periods. Hence, if the particulate matter deposit amount in the DPF is estimated to be larger than the actual deposit amount, the regeneration frequency increases, leading to an increase in energy consumption. If the particulate matter deposit amount in the DPF is estimated to be smaller than the actual deposit amount, the actual particulate matter deposit amount in the DPF exceeds the predetermined amount, and hence the temperature of the DPF must be raised excessively in order to burn the large amount of particulate matter during regeneration, thereby reducing the life of the DPF.
To regenerate the DPF appropriately, the differential pressure must be detected with a high degree of precision. For this purpose, the prior art proposes correcting the value of the differential pressure, detected by the differential pressuresensor, in accordance with the exhaust gas flow rate and DPF temperature.